The present invention relates to a fluid actuator suitable for use in vibration removing of high precision measuring apparatus and semiconductor manufacturing apparatus, for example.
Conventionally, fluid actuators, such as air spring, air cylinder, and hydraulic cylinder, have been well known. In such fluid actuators, while on one hand a supporting load or operating force by the fluid actuator is determined by internal pressure and effective pressure-receiving area, on the other hand the pressure of the fluid to be supplied is limited. Therefore, in order to make it possible to use the fluid actuator in a high load application, there is no other way than enlarging the effective pressure-receiving area.
For example, JP B H7-76576 (examined) and JP A H3-219141(unexamined) disclose apparatuses in which an air spring is used for suppressing vibration. In order to enlarge the force of such air springs, it is necessary to increase the number of air springs.
In the field of precision working, in order to suppress a rise in the cost for maintaining clean environment, it is required that the equipment be made more intensive without exerting bad influence upon precision working. On the other hand, there are demands for larger size and higher speed of the equipment, and this makes it more and more necessary to improve the support capability per unit area and controlling force with respect to the equipment. That is, it is required that a large controlling force be generated in a small space and vibration controllability be improved in a wide frequency range. This poses a problem that it is not possible to increase the number of fluid actuators, and to enlarge the effective pressure-receiving area.
An object of the present invention is to provide a fluid actuator which eliminates the foregoing problem and which can be applied to high loads with small space.
In order to achieve the above object, according to the present invention, there is provided a fluid actuator comprising: a core having a plurality of discs protruding around an output shaft; a cylinder casing which has a body of hollow configuration with an opening provided at its upper portion, and which receives the core in the hollow body in a state where not only an upper end of the output shaft is projected out of the opening but a lower portion of the core is set free, and which has an annular protrusion projecting into an air gap between the discs; an annular small seal member interposed between a portion of the core located between the discs and the annular protrusion so as to allow their relative movement in upward and downward directions and so as to partition upper and lower cavities from one to the other; and an annular large seal member interposed between an inner peripheral surface of the cylinder casing and outer periphery portion of the discs so as to allow their relative movement in upward and downward directions and so as to partition upper and lower cavities from each other, wherein a plurality of small cavities are defined by being partitioned by the small seal member and the large seal member so as to be arrayed vertically, one of a first group of the small cavities in odd-numbered stages counted from a bottom and a second group of the small cavities in even-numbered stages counted from the bottom communicate with the atmosphere and the other of the first group and the second group communicate with one another, at least one small cavity of the other of the first group and the second group communicates with a fluid flow passage for supplying and discharging pressurized fluid, and an effective pressure-receiving area on the large seal member side is larger than an effective pressure-receiving area on the small seal member side in each of the small cavities.
Further, according to the present invention, there is provided a fluid actuator comprising: a core having a plurality of discs protruding around an output shaft; a cylinder casing which has a body of hollow configuration with an opening provided at its upper portion, and which receives the core in the hollow body in a state where not only an upper end of the output shaft is projected out of the opening but a lower portion of the core is set free, and which has an annular protrusion projecting into an air gap between the discs; an annular small seal member interposed between a portion of the core located between the discs and the annular protrusion so as to allow their relative movement in upward and downward directions and so as to partition upper and lower cavities from one to the other; and an annular large seal member interposed between an inner peripheral surface of the cylinder casing and an outer periphery portion of the discs so as to allow their relative movement in upward and downward directions and so as to partition upper and lower cavities from each other, wherein a plurality of small cavities are defined by being partitioned by the small seal member and the large seal member so as to be arrayed vertically, a first group of the small cavities in odd-numbered stages counted from a bottom communicate with one another, at least one small cavity in the first group communicating with a first fluid flow passage for supplying and discharging pressurized fluid, a second group of the small cavities in even-numbered stages counted from the bottom communicate with one another, at least one small cavity in the second group communicating with a second fluid flow passage for supplying and discharging pressurized fluid, and an effective pressure-receiving area on the large seal member side is larger than an effective pressure-receiving area on the small seal member side in each of the small cavities.
Furthermore, according to the present invention, there is provided a fluid actuator comprising: a cylinder casing opened at its upper portion; a core disposed inside the cylinder casing; a small seal member which is interposed between the cylinder casing and the core and which does not interfere with upward and downward relative movement of the cylinder casing and the core; a large seal member which is interposed in alternate relation with the small seal member between the core and the cylinder casing and which does not interfere with upward and downward relative movement of the core and the cylinder casing, and further which has an effective pressure-receiving area larger than that of the small seal member; a fluid flow passage for supplying pressurized fluid to a small cavity defined by the small seal member and the large seal member in odd-numbered stage counted from a bottom, and for discharging the fluid present in the small cavity; and an opening which allows a small cavity defined by the small seal member and the large seal member in even-numbered stage counted from the bottom to communicate with the atmosphere.
Still furthermore, according to the present invention, there is provided a fluid actuator comprising: a cylinder casing opened at its upper portion; a core disposed inside the cylinder casing; a small seal member which is interposed between the cylinder casing and the core and which does not interfere with upward and downward relative movement of the cylinder casing and the core; a large seal member which is interposed in alternate relation with the small seal member between the core and the cylinder casing and which does not interfere with upward and downward relative movement of the core and the cylinder casing, and further which has an effective pressure-receiving area larger than that of the small seal member; an opening which allows a first fluid flow passage to communicate with the atmosphere, the first fluid flow passage serving for supplying pressurized fluid into a small cavity defined by the small seal member and the large seal member in odd-numbered stage counted from a bottom, and for discharging the fluid in this small cavity; and a second fluid flow passage for supplying pressurized fluid to a small cavity defined by the small seal member and the large seal member in even-numbered stage counted from the bottom, and for discharging the fluid in this small cavity.
Still furthermore, according to the present invention, there is provided a fluid actuator comprising: a cylinder casing opened at its upper and lower portions; a core disposed inside the cylinder casing; a small seal member which is interposed between the cylinder casing and the core and which does not interfere with upward and downward relative movement of the cylinder casing and the core; a large seal member which is interposed between the core and the cylinder casing and which does not interfere with upward and downward relative movement of the core and the cylinder casing, and further which has an effective pressure-receiving area larger than that of the small seal member; and a fluid flow passage for supplying pressurized fluid to a small cavity defined by the small seal member and the large seal member and for discharging the fluid in this small cavity.
Still furthermore, according to the present invention, there is provided a fluid actuator comprising: a cylinder casing opened at its upper and lower portions; a core disposed inside the cylinder casing; a small seal member which is interposed between the cylinder casing and the core and which does not interfere with upward and downward relative movement of the cylinder casing and the core; a large seal member which is interposed in alternate relation with the small seal member between the core and the cylinder casing and which does not interfere with upward and downward relative movement of the core and the cylinder casing, and further which has an effective pressure-receiving area larger than that of the small seal member; a fluid flow passage for supplying pressurized fluid to a small cavity defined by the small seal member and the large seal member in one of odd-numbered stage and even-numbered stage counted from a bottom, and for discharging the fluid in this small cavity; and an opening which allows a small cavity, defined by the small seal member and the large seal member in the other of the odd-numbered stage and the even-numbered stage, to communicate with the atmosphere.
Still furthermore, according to the present invention, there is provided a fluid actuator comprising: a cylinder casing opened at its upper and lower portions; a core disposed inside the cylinder casing; a small seal member which is interposed between the cylinder casing and the core and which does not interfere with upward and downward relative movement of the cylinder casing and the core; a large seal member which is interposed in alternate relation with the small seal member between the core and the cylinder casing and which does not interfere with upward and downward relative movement of the core and the cylinder casing, and further which has an effective pressure-receiving area larger than that of the small seal member; a first fluid flow passage for supplying pressurized fluid to a small cavity defined by the small seal member and the large seal member in one of odd-numbered stage and even-numbered stage counted from a bottom, and for discharging the fluid in this small cavity; and a second fluid flow passage for supplying pressurized fluid to a small cavity defined by the small seal member and the large seal member in the other of the odd-numbered stage and even-numbered stage, and for discharging the fluid in this small cavity.